1. Field of the Invention
The present invention relates, in general, to vehicle diagnostic control apparatus and, more particularly, to a vehicle diagnostic control apparatus suitable for use in a hybrid vehicle.
2. Description of Related Art
One known technique for diagnosing exhaust system-related faults uses outputs from an oxygen sensor upstream of, and another oxygen sensor downstream of, a catalyst. The technique then uses a correlation function to quantify similarities in waveforms between the upstream and downstream oxygen sensors, thereby determining deterioration of the catalyst (see, for example, JP-A-6-241026).
In later years, hybrid vehicles using engines and motors to drive the vehicles are becoming popular. Some known technique uses a motor and a reverse ratio of an upstream oxygen sensor and a downstream oxygen sensor to determine the deterioration of the catalyst (see, for example, JP-A-2000-110650).